CoRE is a rule engine for SmartThings. A piston is a rule for something some action based upon some input. See this wiki for help installing the SmartApp:
http://thingsthataresmart.wiki/index.php?title=CoRE#CoRE_SmartApp_Installation
Once you have CoRE installed, you would open the SmartApp and do this to add piston that polls SmartWeather every 15 minutes:
(This is for Android; it may be slightly different on iOS)
- Select “Add a CoRE Piston”
- Scroll up, make sure “Basic” is selected
- Select “If…”
- Select “Add a condition”
- Select “Capability”; scroll down and select “Time”
- Select “Comparison”; then select “Happens At”
- Select “Value”; scroll down and select “Every number of minutes”
- Change the number of minutes from the default 5 to 15
- Select “Done” to finish the trigger
- Select “Done” to finish the condition group
- Select “Then…”
- Select “Add an action”
- scroll down and select “Control any device”
- scroll down and select “Select pollable devices”
- scroll down and select “SmartWeather” then “Done” twice
- Select “Add a task”
- Select “Poll” and then Done twice
- Select one last Done to save the piston